In recent years, a non-contact power supply system for supplying power in a non-contact manner is being popular. The non-contact power supply system uses electromagnetic coupling such as electromagnetic induction or magnetic field resonance to supply power to a power reception apparatus such as a portable terminal, a tablet terminal and the like in a non-contact manner. In general, the non-contact power supply system is composed of a power transmission apparatus and a power reception apparatus, and in the power transmission apparatus, a power transmission coil and a power transmission circuit for supplying power are included. On the other hand, in the power reception apparatus, a power reception coil for receiving power from the power transmission apparatus in a non-contact manner, a voltage conversion circuit for using the received power for drive of the power reception apparatus itself, and a charging circuit for charging a secondary battery carried in the power reception apparatus itself are included.
It is necessary that the non-contact power supply system increases Q values of the power transmission coil and the power reception coil in order to be capable of supplying power to the power reception apparatus even if the power transmission apparatus is separated from the power reception apparatus by 1-2 cm or more. Thus, a frequency of a few MHz or more (for example, 6.78 MHz or 13.56 MHz) capable of increasing the Q values of the coils is used as a frequency of AC power output by the power transmission apparatus. If the Q values of the coils are increased, even if a distance between the power transmission coil and the power reception coil is large, characteristics capable of efficiently supplying power are obtained.
The power reception apparatus constitutes a LC resonance circuit with the power reception coil and a resonance capacitor, and can efficiently receive the AC power output by the power transmission apparatus by being designed to reduce impedance of the LC resonance circuit. The AC power supplied to the power reception apparatus is converted to DC power through a rectifier circuit. The power to which the DC conversion is carried out through the rectifier circuit is used by being converted to a voltage required for the drive of the power reception apparatus itself through the voltage conversion circuit.
Incidentally, as the rectifier circuit, in general, a diode full-wave rectifier circuit is used; however, harmonic noise is generated from the diode full-wave rectifier circuit as junction capacitance Cj is included in a diode. In other words, an equivalent circuit at the time a reverse voltage is applied to a diode can be simulated as a configuration in which resistance of a fraction of Ω and junction capacitance Cj (capacitor) of dozens of pF are connected in series.
Thus, immediately after a switching point at which the reverse voltage is applied to the diode from a state in which a forward voltage is applied thereto, the junction capacitance Cj of the diode is rapidly charged, and a large current flows in a short time to generate the harmonic noise. The generated harmonic noise is radiated from the power reception coil of the power reception apparatus.
In the non-contact power supply system which can supply the power to the power reception apparatus even if the power transmission coil is separated from the power reception coil by a few cm, as the power reception coil and the power transmission coil are not closely combined, an electromagnetic wave including the harmonic noise is easily radiated from the power reception coil to a space. Therefore, it is necessary to reduce the harmonic noise generated from the diode full-wave rectifier circuit in order to reduce the electromagnetic wave including the harmonic noise output from the power reception coil.
As an example of a countermeasure of the harmonic noise of the power reception apparatus, a wireless power reception apparatus disclosed in Japanese Translation of PCT International Application Publication No. JP-T-2014-530592 is known. The power reception apparatus disclosed in Japanese Translation of POT International Application Publication No. JP-T-2014-530592 arranges a band-stop filter circuit between the diode full-wave rectifier circuit and a smoothing capacitor to electrically insulate radiation from a rectifier.
However, it is difficult that the capacitor of the band-stop filter circuit carries out the same work as the junction capacitance Cj of the diode of the rectifier and reduces the harmonic noise. Further, in a case of reducing the capacitor of the band-stop filter circuit to the utmost and constituting the capacitor of the band-stop filter circuit with only an inductor, a large inductor is required for noise reduction. Thus, a sufficient current cannot be supplied to a load circuit, and as a result, output power of the power reception apparatus falls.